Home Energy: Insulation

Insulation effectiveness is measured by its R-value, which indicates resistance to heat flow. The higher the R-value, the better the insulation.

For Maryland homes, the U.S. Department of Energy recommends the following minimum R-values for existing homes:

• Attics: R-49 to R-60
• Floors: R-25 to R-30
• Exterior Walls: R-13 to R-21 (depending on wall construction)

These values can vary based on your home's age, construction type, and whether you're upgrading or building new.

1. Batts, Blankets, and Rolls

These are pre-cut or roll-form insulation products made from fiberglass or mineral wool. They’re ideal for open framing in attics, basements, and crawl spaces. R-values range from 2.2 to 3.2 per inch for fiberglass and around 3.1 per inch for mineral wool.

• Available with or without vapor barriers (kraft paper or foil)
• Must be installed without compression to maintain effectiveness
• Require fire-resistant covering if vapor barrier is present

2. Loose-Fill (Blown-In)

Made from cellulose, fiberglass, or mineral wool, loose-fill insulation is blown into attics or wall cavities using special equipment. It’s especially useful for retrofitting older homes.

• Cellulose: ~3.7 R-value per inch
• Fiberglass: ~2.2 R-value per inch
• Must be installed to proper density to prevent settling

3. Rigid Foam Board

These boards are made from materials like expanded or extruded polystyrene, polyurethane, or polyisocyanurate. They offer high R-values—up to 7.5 per inch—and are commonly used in basements, crawl spaces, and under siding.

• Must be covered with a fire-resistant barrier indoors
• Extruded polystyrene is preferred for below-grade applications

4. Spray Foam (Foamed-in-Place)

Spray foam insulation, typically polyurethane, is applied by professionals and expands to fill cavities. It provides excellent air sealing and moisture resistance.

• R-value: ~6 per inch
• Acts as both insulation and air barrier
• Ideal for hard-to-reach areas or irregular spaces

Best Practices for Maryland Homes

• Seal Before You Insulate: Air leaks around windows, doors, and framing can undermine insulation. Use caulk or spray foam to seal gaps before adding insulation.
• Use Vapor Barriers Wisely: In Maryland’s humid climate, vapor barriers help prevent moisture buildup that can damage insulation and structures.
• Ensure Proper Ventilation: Especially in attics and crawl spaces, ventilation is key to preventing moisture problems and maintaining indoor air quality.

Quick Reference: R-Values by Material

R-value measures how well insulation resists heat flow—the higher the number, the better the performance. Common attic insulation materials include:

• Fiberglass batts or blankets: ~3.2 R-value per inch
• Loose-fill cellulose: ~3.7 R-value per inch

To reach R-49:

• You’d need about 15 inches of fiberglass batts
• Or approximately 13 inches of loose-fill cellulose

Unfinished Attic

This is the most common and easiest type to insulate. The attic is not part of the living space and is typically accessed through a hatch in a hallway or closet. Insulation is installed between the floor joists (which also serve as the ceiling of the living space below). Homeowners with basic DIY skills can often handle this project, especially with guidance from a professional or local Extension office.

Finished Attic

In homes where the attic includes living space, insulation must be added to:

• Kneewalls (short vertical walls)
• Ceilings under the roof
• Floors of unconditioned spaces adjacent to the finished area

This type of project often requires multiple insulation materials and specialized equipment, so it’s best handled by a professional.

Flat, Vaulted, or Cathedral Ceilings

These ceiling types typically have little or no attic space above them, making insulation more challenging. If space allows, insulation can be blown or placed between the ceiling and roof. Proper ventilation and air sealing are essential to prevent moisture buildup. These projects also usually require professional installation.

Properly insulating your unfinished attic is one of the most cost-effective ways to improve your home’s energy efficiency. Here’s how to do it safely and effectively:

1. Investigate Your Attic

Before you begin, inspect your attic to assess its current condition:

• Access the attic using a ladder through a ceiling hatch (usually in a hallway or closet).
• Wear protective gear: a dust mask or respirator, gloves, and long sleeves.
• Lay boards across joists to create a safe walkway—never step between joists, as the ceiling below may not support your weight.
• Check existing insulation: Measure its depth and identify the type (fiberglass, cellulose, mineral wool, etc.). If it’s dry and evenly spread, you can add more on top.
• Watch for vermiculite insulation: If present, stop and have it tested for asbestos by a certified professional. (More info: EPA Vermiculite Guide)

2. Inspect Electrical Wiring

• Look for exposed wires or open junction boxes. These must be corrected before adding insulation.
• Knob-and-tube wiring (common in older homes) should never be covered with insulation. If present, consult a licensed electrician for an upgrade.

3. Seal Air Leaks

Insulation alone won’t stop heat loss if air is leaking into the attic. Seal gaps and cracks first:

• Common leak points: around plumbing stacks, recessed lights, wiring holes, ductwork, and wall tops.
• Use caulk or spray foam to seal small gaps.
• Install weatherstripping around the attic hatch to prevent drafts.

4. Install a Vapor Barrier (If Needed)

Moisture from inside your home can rise into the attic and condense, reducing insulation effectiveness and causing mold or rot.

• For first-time insulation: Lay a vapor barrier (like polyethylene plastic) on the attic floor before adding insulation, or use kraft-faced batts with the vapor barrier facing the living space.
• If insulation already exists: Do not add a second vapor barrier. Use unfaced insulation or remove/slash any vapor barrier on new batts to prevent moisture trapping.
• Alternative: Use vapor-retardant paint on ceilings in high-moisture rooms (kitchens, bathrooms, laundry areas).

5. Ensure Proper Ventilation

Ventilation prevents moisture buildup and helps regulate attic temperature.

• With a vapor barrier: Provide 1 square foot of vent area per 300 square feet of attic floor.
• Without a vapor barrier: Double the vent area (1 square foot per 150 square feet).
• Use a mix of vents: Soffit (low) and ridge or gable (high) vents allow for effective cross-ventilation.
• Install baffles or chutes to keep insulation from blocking soffit vents.

6. Install the Insulation

Now you’re ready to insulate:

• Batts or rolls: Fit snugly between joists. Lay a second layer perpendicular to the first for added R-value.
• Loose-fill: Pour or blow in evenly. Use a rake or board to level. Add depth markers if going above joist height.
• Combination approach: Use batts in open areas and loose-fill in tight or irregular spaces.

Important safety tips:

• Keep insulation 3 inches away from recessed lights, chimneys, flues, and fan motors.
• Use sheet metal barriers around heat sources, extending 4 inches above the insulation.
• Consult a professional if your attic contains a furnace, water heater, or knob-and-tube wiring.

Insulating your attic may be dusty and time-consuming, but it’s one of the most effective ways to improve comfort and reduce energy costs in Maryland homes. Whether you DIY or hire a contractor, following these steps ensures a safe, efficient, and long-lasting result.

For Maryland homes, the U.S. Department of Energy recommends insulating exterior walls to at least R-13 to R-21, depending on the wall construction and whether you're retrofitting or building new. Common materials for wall insulation include, 

• Fiberglass batts or blankets: R-value ~3.2 per inch
• Loose-fill cellulose: R-value ~3.7 per inch
• Rigid foam board (e.g., polystyrene): R-value ~4.5 to 5.5 per inch

The best insulation type depends on your wall structure and whether you're insulating from the inside, outside, or within existing cavities.

To determine if your walls can be insulated:

• Remove a light switch or outlet cover (after turning off power) and inspect the cavity.
• In the attic, look for exposed wall tops—wood framing indicates cavity walls, while solid masonry suggests no cavity.

If your walls already contain insulation, adding more may not be cost-effective. But if they’re empty, your home is a strong candidate for wall insulation.

There are three main approaches to insulating exterior walls in existing Maryland homes:

1. Blow insulation into existing wall cavities
   This is the most cost-effective and least disruptive method, especially if your home has framed walls with empty cavities. A contractor drills small holes in the siding or sheathing and uses a blower to fill the cavities with loose-fill insulation.
2. Add insulation to the exterior before re-siding
   If you're planning to replace your siding, this is a great opportunity to add rigid foam board insulation beneath the new exterior finish.
3. Insulate from the interior
   Typically used in unfinished basements, this involves adding insulation between new framing and finishing with drywall.

Wall insulation is best handled by professionals to ensure proper density and full cavity coverage. In Maryland, income-qualified households may be eligible for free weatherization services, including wall insulation. Contact your local utility or community action agency for details.

What to Expect During Installation

• Contractors inspect walls for moisture issues and structural integrity.
• Holes are drilled through siding or sheathing to access wall cavities.
• Insulation (typically cellulose, fiberglass, or mineral wool) is blown in and packed to the correct density.
• Holes are sealed and siding is restored. If siding removal isn’t feasible, holes may be drilled directly into the siding and plugged afterward.

Special Wall Types

• Brick or stone veneer with cavities: May be insulatable from the attic or other access points.
• Solid masonry or concrete walls: Require insulation to be added to the interior or exterior surface using rigid foam or framed batts.

Important considerations:

• Always place insulation on the cold side of plumbing to prevent freezing.
• Avoid vapor barriers on below-grade walls to prevent moisture trapping.
• Rigid foam must be covered with a fire-resistant material like drywall.